Precast reinforced concrete structures of the type having double reinforcing cages of welded steel wire reinforcement use spacers to connect the inner and outer reinforcement cages at a predetermined spacing from each other and to hold the interconnected cages at predetermined spacings from the inner or outer form or from both the inner and outer forms so as to provide the required cover of concrete over the steel wire reinforcement cages. One type of spacer, which is generally called a box spacer, is a length of steel wire that is bent at each end to form a shallow seat for the oppositely located wires of the inner and outer reinforcement cages and, outwardly of each wire seat, a spacer loop. The box spacer straddles the two cage wires that it connects, the cage wires being located inwardly of the spacer loops.
An adaptation of the aforementioned box spacer is a stirrup spacer used in double cage reinforced round pipe, wherein the inner reinforcement cage is formed into a hoop of the required diameter and is geometrically stable. The outer reinforcement cage is pre-curved to a relaxed (unloaded) diameter greater than its final diameter. When the stirrup spacers are installed, the outer cage is pre-stressed such as to pull the wires of the outer cage inwardly into the outer seats of the spacers. The resiliency and tension between the circumferential wires of the inner and outer cages keeps the circumferential wires that are connected by the stirrup spacers from displacing toward the wires of the other cage. It is, therefore, not necessary to separately fasten the stirrup spacers to the cages, such as by welding or by tie wires.
When box spacers are used for precast reinforced concrete box sections, it is necessary to secure the wires of the inner and outer reinforcement cages to the spacers to prevent the cages from being displaced from their seats toward each other when the concrete is poured. One way of doing that is by welding the box spacers to the two cages. Welding is laborious and costly and is sometimes not permitted under the specifications for the product, inasmuch as welding weakens both the wires of the reinforcement cages and the spacers. When welding is not permissible, small soft tie wires are used at the juncture between each spacer and each reinforcing cage wire. Tie wires also require additional labor and, because they are relatively weak, can fail and allow displacements of the reinforcement cages toward each other during pouring of the concrete.
U.S. Pat. No. 4,999,965 ("the '965 patent") describes and shows a weldless spacer for the reinforcements of double cage reinforced concrete products. The spacer of the '965 patent, which is commercially available, is a length of spring steel wire that has a shallow wire-spacing loop at each end of a straight bridging or spanning portion that extends between the inner and outer reinforcement cages (the opposite wires of the reinforcement cages nest in such wire-spacing loops) a form-spacing loop outwardly of each wire-spacing loop with respect to the spanning portion, and a retainer hook that is bent back from the form-spacing loop and hooks onto the cage wire. Each wire-spacing loop overlies the wire, and each retainer hook underlies the wire. The wire-spacing loops are offset from the retainer hooks longitudinally of the wires of the reinforcement cages to which the spacer is connected.
The '965 patent spacer is installed by laying it obliquely to one of the wires of a reinforcement cage and hooking one end to that wire, pivoting the spacer so that it lies nearly perpendicular to the two reinforcement wires, and prying the still unhooked end with a tool placed between the wire-spacing loop and the retainer hook to twist the retainer hook outwardly and downwardly so that it can be forcibly pried into place under the cage wire. Setting the retainer hook requires prying the hook outwardly by expanding and laterally deflecting the form-spacer loop. A relatively large force is required, because there is very little leverage distance afforded by the form-spacing loop. It is easy for the tool to slip from the retainer hook when the installer is trying to secure the hook, thus releasing the stress and allowing the unhooked end to spring free violently. The spacer can strike the user's hands or body if he is not careful. The need to use a tool and to apply a very large torsional force to the hook makes installation very strenuous and hazardous.